This invention relates to a method of making field-emitter structures using semiconductor micromachining techniques.
Field-emitter structures are metallic structures with extremely small protruding points with radii ranging from approximately 20 A to 3000 A. Emission of electrons into a vacuum from a field-emitter occurs via quantum mechanical tunneling through the barrier whose width is determined by the enhanced local electric field at the tip. Field-emitters are useful in field ionizers, scanning tunnel microscopes, electron guns, and field emitter vacuum integrated circuits.
Field-emitters have been formed by depositing metal onto etched silicon which has been shaped into a pyramid or funnel shaped projection. U.S. Pat. No. 3,665,241 to Spindt describes such a field emitter. In Spindt the metal is evaporated onto a mold having holes formed by electron beam lithography. The shape of the field emitter is built-up by rotating the mold and by using multiple evaporation sources. Not only is Spindt's technique cumbersome, but also because of the varying distances from the evaporation sources, the field emitters produced do not have the same uniform structure. Furthermore, it is extremely difficult to coat silicon with a metal by sputtering or e-beam evaporation and to obtain good adhesion of the metal to the silicon near the tip of the emitter.
U.S. Pat. No. 4,307,507 to Gray, et al. overcomes some of the problems associated with mold rotation and deposition onto silicon. Gray's method etches emitter shaped cavities into a silicon substrate, back-fills them with a metal and then etches away the silicon leaving a solid metal emitter. Alternatively Gray provides that a passivation layer of silicon dioxide or silicon nitride is deposited on the etched silicon prior to filling with metal. While Gray's method offers advantages over Spindt's method, Gray's method produces only solid metal emitter structures and requires numerous processing steps.
Therefore, it is an object of the present invention to provide a method of making a field emitter structure requiring a minimum number of processing steps.
It is another object of the invention to provide a method of making a field emitter structure which will produce a solid metal emitter or a thin layer a metal on a solid silicon substrate emitter.
It is yet another object of the invention to provide a method of making a field emitter structure which is capable of good process control and reproducible results.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.